Neuroplasticity is a key mechanism underlying post-stroke recovery of motor function. Brain imaging research provides evidence that these beneficial neural changes are experience-dependent and therefore related to rehabilitative interventions that target movement deficits. Recently, non-invasive brain stimulation has been identified as a means to improve the neurophysiological conditions for neuroplasticity to occur in ways that enhance, support and accelerate the rehabilitation process. The Pi's previous work has demonstrated the therapeutic potential of lesioned-hemisphere repetitive transcranial magnetic stimulation (LH-rTMS) as a therapy-adjuvant to improve paretic upper extremity (UE) function post-stroke. Other groups have similarly shown that non-lesioned hemisphere rTMS (NLH-rTMS) also improves paretic UE movement. Thus, there is controversy over which hemisphere is the better target of rTMS. We have argued that LH-rTMS promotes increased motor cortex (MC) activation supporting motor re-learning, while others have argued that NLH-rTMS inhibits the negative influences that the NLH exerts on the LH via excessive transcallosal inhibition. To date, no study has tested LH-rTMS against NLH-rTMS in the chronic post-stroke recovery phase. Although we hypothesize that the LH is the better target to promote motor re-learning and recovery-related neuroplasticity, we must test this hypothesis before moving to a large clinical trial on LH-rTMS. The goal of the proposed project is to directly evaluate the differences in the efficacy of LH-rTMS vs. NLH-rTMS. This project will provide the first-ever evidence on the effects of LH-rTMS vs. NLH-rTMS through the integration of a comprehensive set of brain imaging, neurophysiological and motor performance outcome assessments. We hypothesize that LH-rTMS will produce significantly greater motor improvements and neurological changes than NLH-rTMS. This hypothesis will be tested in a prospective, stimulation+rehabilitation design in which 40 chronic stroke survivors will be randomized to 4 weeks of either LH-rTMS or NLH-rTMS, each of which will be combined with task-oriented rehabilitation that will immediately follow each daily dose of rTMS. The aims are to: 1) Determine the differential effects of LH-rTMS vs. NLH rTMS on a range of upper limb motor function outcomes in survivors of stroke, and 2) Determine the differential effects of LH-rTMS vs. NLH rTMS on neurophysiological and neuroimaging markers of neuroplasticity outcomes.